inbox: use pgp encryption (#70)

* inbox: use pgp encryption && other fixes
* fix inbox key last used at time
* remove inbox items if keys change or same item id syncs

* inbox:update inbox sync item
* rename item field to sync
* add alg field

* sync: delete inbox items after commit succeeds

* user: merge if conditions

---------

Co-authored-by: Abdullah Atta <abdullahatta@streetwriters.co>

Notesnook.API/Services/UserService.cs

@@ -184,6 +184,8 @@ namespace Notesnook.API.Services
                     };
                     await Repositories.InboxApiKey.InsertAsync(defaultInboxKey);
                 }
+
+                await Repositories.InboxItems.DeleteManyAsync(t => t.UserId == userId);
             }
 
             await Repositories.UsersSettings.UpdateAsync(userSettings.Id, userSettings);